Treatment of textile wastewaters by solar-driven advanced oxidation processes

Heterogeneous (TiO2/UV, TiO2/H2O2/UV) and homogenous (H2O2/UV, Fe2+/H2O2/UV) solar advanced oxidation processes (AOPs) are proposed for the treatment of recalcitrant textile wastewater at pilot-plant scale with compound parabolic collectors (CPCs). The textile wastewater presents a lilac colour, with a maximum absorbance peak at 516 nm, high pH (pH = 11), moderate organic content (DOC = 382 mg C L−1, COD = 1020 mg O2 L−1) and high conductivity (13.6 mS cm−1), associated with a high concentration of chloride (4.7 g Cl− L−1). The DOC abatement is similar for the H2O2/UV and TiO2/UV processes, corresponding only to 30% and 36% mineralization after 190 kJUV L−1. The addition of H2O2 to TiO2/UV system increased the initial degradation rate more than seven times, leading to 90% mineralization after exposure to 100 kJUV L−1. All the processes using H2O2 contributed to an effective decolourisation, but the most efficient process for decolourisation and mineralization was the solar-photo-Fenton with an optimum catalyst concentration of 100 mg Fe2+ L−1, leading to 98% decolourisation and 89% mineralization after 7.2 and 49.1 kJUV L−1, respectively. According to the Zahn–Wellens test, the energy dose necessary to achieve a biodegradable effluent after the solar-photo-Fenton process with 100 mg Fe2+ L−1 is 12 kJUV L−1.

► Solar photo-Fenton reaction enhances the biodegradability of textile wastewaters.
► Solar AOPs are robust methods of purifying textile wastewaters at lower cost and with less energy.
► AOPs become even more attractive if they can use solar energy, which is a relevant resource in most countries with high textile industry.